Hi Melanie:

You want to add these lines to /etc/ssh/sshd_config instead of /etc/ssh/ssh_config since you want to control the activity of the sshd daemon. Be sure to stop/restart the sshd daemon on the machine that is serving up sftp after you have saved your changes (/etc/init.d/sshd restart). You should then be able to log in on your client machine. Best of luck!!